engleski

The electric parameters in interfacing of transparent conductive and charge transfer layers in solar cells

Majority of solar cells are assembled on transparent conductive layers deposited on substrate, whereas these layers are concerned as critical ones for enabling high efficiency electron transport between dye and electrode. Transparent conductive layers roughness ensures active material can be thin enough to overcome the problem of low lifetime of photogenerated carriers ; the optical gap and surface chemistry determine transfer of photo generated carriers towards the external circuit, while both influence the efficiency and stability of all type of solar cells, especially organic. In multilayer solar cells nominate electrical and structural compatibility of active and passive layers as the most important task is optical, where the various nanostructural forms of inorganic materials of in different crystal sizes in hybrid solar cells, like the TiO2 nanotube arrays, may allow additional tuning of the optical and electrical properties. We prepared ordered TiO2 or ZnO nanoarrays and nanotubes architectures as candidates for dye sensitized solar cell and hybrid organic photovoltaic devices as electron accepting and extracting layers. Ti anodization process was introduced as a convenient way to produce the TiO2 NT with various geometries. Magnetron deposition with surface processing was responsible for ZnO nanostructured surfaces. Several of nanostructures were infiltrated with organic absorbers. The role of interfacial phenomena surface conditions, morphologies and processing responsible for solar cell performance and overall stability was focused. It was found the prepared samples yield some difference in surface morphologies and therefore interface properties. Growth of the TiO2 NT is known to depend on the basic anodization parameters. So for advanced application precise tailoring of numerous parameters is required. In order to enable these upgrades layers were investigated for structural type, microstructure, surface condition, geometry. Thin film layers of the sputtered Ti, ZnO even glass substrate and their interaction were identified as additional factors determining the final composite properties in our investigation. Electron microscopy was used to evaluate the layers. Photoluminescence spectroscopy on hybrid non-contacted samples was performed to observe charge transfer mechanism, while photoinduced absorption revealed information on kinetics of excited states of carrier. The electrical properties in the dark and under illumination was studied using impedance spectroscopy (0.1 Hz – 1 MHz) show the role of dielectric properties and identifying relevant time scales for electronic transport and recombination. Our goal was to check the applicability of the proposed transparent conductive layers and charge transfer layers using different synthesis procedures and surface processing yielding a variety of nano-structured thin films to be infiltrated with different organic absorbers to identify optimized parameters for realizing efficient charge separation at hybrid interfaces. It was found the changes in electric behaviour depend on the anodization process and are further related (could be correlated) to the glass substrate, ZnO and TiO2 NT layers structural and morphological properties. This work offer valuable date on the often used layers for the preparation of DSSC solar cell. Best samples containing of glass substrate - ZnO thin film - Ti thin film - TiO2 NT thin film layers were found to be favourable for the solar cell assembly. The investigation should offers deeper understanding of what limits charge separation at hybrid interfaces, a fundamental question in the literature.

TiO2 NT; OPV Solar Cells; Anodization; Characterization

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